The present invention relates to a dental appliance for introducing a filler material into tooth cavities.
More particularly, it relates to a dental appliance which has a filler pipe, a filler expelling element which is reciprocable in a first passage and merges into the filler pipe, a replaceable magazine which extends transversely to the filler pipe and opens into the latter, so that a part of the filler material such as amalgam is pressed from the magazine via a second passage by a magazine expelling element in a working stroke which starts above the opening of the magazine and ends at the outlet of the filler pipe, so as to press the part of the filler material into the filler pipe. A mechanical transmission couples the filler expelling element and the magazine expelling element surrounded by a common housing so as to coordinate their movements. A toothed rack is connected with the magazine expelling element and forms a part of the above mechanical transmission.
A known dental appliance of this type is disclosed, for example, in the German Patent No. 2,364,547. It is characterized by a mechanical transmission which is driveable from a power source, on the one hand, and by a pneumatic drive which is set into operation from a pressure air source. In addition to the complicated construction, the above mentioned dental appliance is dependent from an energy source which is connectable with it via a connecting conduit. The connecting conduit considerably affects the ergonomy and manipulation of the appliance, and on the other hand the requirement of an energy source limits the operational region of such an appliance in a medical practice. Finally, after emptying of the magazine, a new magazine must be inserted promptly, or treatment must continue with a second appliance.
U.S. Pat. No. 3,792,530 discloses a further appliance of a different type in which a filler expelling element is guided with a play in a guiding passage by means of a piston arranged at its front end, and a magazine expelling element is guided in a second guiding passage by a further piston. The filler expelling element and the magazine expelling element are acted upon at their rear ends by the force of springs. These springs have the purpose of holding the piston of the filler expelling element in a withdrawn position from the filler pipe inside an inner space of an opening, until the slider engaging the rear end of the filler expelling element is manually moved forwardly. The spring has the purpose of pressing the filler material from the second guiding passage which serves as a reserve container, into the upper hollow space of the filler pipe. The rear end of the magazine expelling element is provided with a toothed rack which engages with a bracket arranged on the rear end of the slider. Thereby the movement of the magazine expelling element is prevented as long as the filler expelling element, by releasing the finger pressure on the slider, is withdrawn under the action of its spring. The withdrawal of the magazine expelling element for a new filling of the magazine which is formed here as a tilting magazine and not an exchange magazine, is performed via a slider extending through the housing with a return pulling applied by a spring against the magazine expelling element. In this dental appliance the movements and the movements sequence of the magazine expelling element, on the one hand, and the filler expelling element, on the other hand, are neither coupled with one another, nor coordinated with one another. Both movements are performed completely independently from one another and the magazine expelling element is arranged under the action of the force applied by one spring, while the filler expelling element is arranged under the action of the force of the expelling button. In the moment of displacement of the filler expelling element, the bracket serves for lifting the action of the spring force which acts upon the magazine expelling element.
The spring which acts upon the magazine expelling element reduces its tension with emptying the magazine. Thereby the amalgam portions which are pressed by the magazine expelling element into the filler pipe are respectively degressively declined. The pre-tensioning of this magazine expelling element must be relatively high, whereby the slider because of the bracket connection between the filler expelling element and the magazine expelling element, must be displaced against a relatively high force of two pre-tensioned springs. Moreover, it is disadvantageous that for filling of the not removed magazine the dentist must return the dental appliance to its idling for filling and then either work with a second dental applicance or wait for the filling of the first dental appliance. This complicated and time consuming operational mode is especially questionable when within the frame of long-time treatment during filling of several teeth, a settling of repeated dry placements of the working field are required.
Finally, this dental appliance does not take into consideration the properties of many filler materials which are used presently in form of a silver amalgam, as these materials approximately in 5-7 minutes after mixing lose their plasticity, and the filling process must be finished within this short time period. Then, a hardening time of several hours follows. This means that the amalgam in question must be brought during a plasticizing time of approximately 5 minutes into the respective filling appliance, discharged from the filling appliance into the tooth cavity, then distributed and condensed in it.
Since in the tilting magazine of the U.S. Pat. No. 3,792,530 after the displacement of the rearwardly engaging piston of the magazine expelling element a hardened amalgam-embossement is located, withdrawal of both axes similarly to the respectively formed front end of the filler expelling element must be performed positively on hindrance.
Finally, U.S. Pat. No. 3,221,409 discloses a dental appliance of a different type. Here, a flat spring which engages a toothed rack of a filler expelling element displaces, by means of relatively high pulling knee lever, a filler expelling element in a housing formed in accordance with the principle of an injection device. Thereby, amalgam is pressed from a filler pipe which is coupled at the front end of the injection device and is replaceable. This appliance is suitable for discharge of amalgam, but not in individual small amalgam portions discharged for condensation, since within the front end of the filler expelling element and the condensing amalgam there is always a further not discharged amalgam in the filler pipe. Since, moreover, pressing forces are always applied via the entire amalgam column between the front end of the filler pipe and the discharge opening of the filler pipe, a precondensation takes place and because of the produced discharge of mercury a fast hardening takes place. This is connected with a direct prehardening and a respective depositing of the amalgam in the filler pipe.